1. Field of the Invention
The present invention relates to an ink tank and, in particular, to a configuration of an air communication passage for establishing a communication of the inside of an ink reserving chamber of an ink tank with outside air.
2. Description of the Related Art
An air communication passage is used for establishing a communication of the inside of a reserving chamber of an ink tank with the outside of the tank, and thereby relieving an increase in the negative pressure caused by a decrease in the amount of ink in the reserving chamber occurring along with the consumption of the ink. This mechanism continuously ensures an appropriate ink supply. Further, even when the pressure in the ink reserving chamber increases or decreases owing to a change in the temperature, etc., of the environment, this pressure change can be similarly alleviated via a the air communication passage.
By the way, since the air communication passage establishes the communication of the ink reserving chamber with the outside air, the passage basically allows the ink solvent to evaporate therethrough. This ink evaporation causes a problem such as an increase in the concentration of the ink color material and solidification of the ink. Further, for example, in a case where a strong impact acts on the ink tank and thereby causing a sudden pressure change in the reserving chamber, the ink may leak via the passage. In order to reduce such ink evaporation and prevent such ink leakage, a configuration is known where an absorber or an air-permeable membrane is provided in a part of the air communication passage. Another configuration is also known where an air communication passage is formed in the shape of a thin and long passage, which maybe used in addition to or independently of preceding configuration.
From the perspective of space permitting the formation of such a particularly long passage in an ink tank, Japanese Patent Application Laid-open No. 4-144755(1992) describes a configuration where a communication passage is formed in an upper cover serving as a case member forming a reserving chamber of an ink tank. More specifically, an air vent hole is formed in the upper cover therethrough to communicate with the reserving chamber. Then, an air vent groove is formed along the surface of the upper cover therein such that the one end of the groove is connected to the air vent hole. Then, a seal member is attached onto the upper cover such as to cover the air vent groove except for the other end thereof used as a vent hole for a communication with the outside air. As a result, a long communication passage is formed.
In an ink tank of the type where ink is stored as it is without any ink absorber in the ink reserving chamber, a configuration is known where ink is supplied to a printing head by means of a pressure regulator valve (hereinafter, referred to simply as a valve, in some cases) having a simple configuration. In the ink tank of this type, the ink passage extending from the ink reserving chamber through the pressure regulator valve to an ink outlet may be formed in the shape of a relatively long passage in some cases. The purpose of this is that the flow resistance in such a long passage assists the function of the simple pressure regulator valve so as to generate a negative pressure (dynamic negative pressure) during ink supply, or alternatively that the above-mentioned passage is formed at the bottom of the ink tank for using the ink all up.
Also in such a relatively long ink passage extending from the ink reserving chamber to the ink outlet, from the perspective of space permitting its formation, a part of the passage may be formed similarly to the above-mentioned air communication passage, that is, by forming a groove in a case member of the ink tank and then covering it with a film. However, the film is attached to the case member generally by fusion bonding, etc. This requires a great amount of labor in comparison with other processes such as ink injection and valve insertion in the ink tank manufacturing. Thus, the formation of the air communication passage and the ink passage by attaching a seal or a film onto a case member having grooves formed thereon has a problem that the number of manufacturing processes increases and hence necessary labor increases particularly.